Flanking the Queen was her husband of 68 years, Prince Philip, who was marking his own special milestone too – he turned 95 on Friday.

Kate, in a “Julia” wool crepe coat that designer Catherine Walker & Co. described as “mist blue”, and a hat by Jane Taylor, arrived with William and brother-in-law Prince Harry and had to wait – chatting with royal relatives.

Prince William and Princess Kate

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Prince Philip, Duke of Edinburgh, and Queen Elizabeth II

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That’s because the principal royal couple arrived about 10 minutes late, as their convoy from Buckingham Palace was caught up in traffic problems caused by a car accident.

At the arrival at the Great West Door, the Queen appeared to joke about it with the welcoming clergy. She had walked up the 24 steps of the magnificent 17th century cathedral and, eyewitnesses said, only barely touched the handrail that had been specially-installed in case she or Philip needed it.

Inside, William sat chatting and laughing with step-mother Camilla, Duchess of Cornwall (in a blue silk dress and coat by Bruce Oldfield and a Philip Treacy hat) as she joined Prince Charles, while his brother Harry turned to uncle Prince Edward, who was with his wife Sophie, and children Lord Severn and Lady Louise.

One commentator, Robert Hardman, said the event had the feeling of a “family wedding.”

The Queen and Philip’s dual birthdays had been heralded by the palace late Thursday when the last of a series of portraits were released, showing them shoulder-to-shoulder as they have been for almost seven decades.

Queen Elizabeth II

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Among the massive turnout of more than 50 members of the extended royal clan, there was also Prince Andrew and his daughters Princesses Beatrice and Eugenie and the Queen’s only daughter Princess Anne, her husband. Her children Peter Phillips and wife Autumn and Zara Tindall and husband Mike completed the main line-up of royals.

The service is the beginning of three days of events to mark the Queen’s official birthday celebrations (she turned 90 in April). On Saturday, the family will be out in force for the Trooping the Colour parade – with Princess Charlotte and Prince George likely waving from the balcony of Buckingham Palace – and then the Patron’s Lunch, for 10,000 people from charities and causes associated with the Queen taking place on Sunday.

Prince Harry

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Led by the Archbishop of Canterbury Justin Welby (who said she had “you have given wonderfully in service to this nation”), there were senior politicians, diplomats and governors-general (who represent the Queen in Commonwealth countries) representing the Queen’s public life.

But there were poignantly-chosen prayers too, read by six people, including one of whom was born on the same day as the Queen. Hilda Price from Cardiff, who is the widow of an Anglican Priest and a leading light in the Mother s Union, was born on the same day as the Queen, April 21, 1926.

Another prayer reader was Clare Balding, whose family has trained some of the Queen s horses. She is a BBC racing commentator and represents the monarch’s love of the sport.

Broadcaster Sir David Attenborough, who turned 90 in May, read a reflection on “passing of the years from the point of view of one born in 1926,” which was written by the creator of the Paddington Bear books, Michael Bond, who turned 90 in January.

Quoting the Queen’s father King George VI just after Britain had gone to war in 1939, he spoke seriously about the landmark moments of the time, and more light-heartedly about growing up in the 1920s and 1930s.